An openwork nickel structure having a high surface area to volume ratio and a porosity which is largely independent of the degree to which the metal structure may be compressed, is formed by depositing on a pyrolyzable support, preferably a reticulated open-pore polyurethane support, a coating of metal by arc-striking utilizing at least one electrode of that metal and by bringing the electrodes out of contact with one another. The metal-covered support is then subjected to pyrolysis to form the metal skeleton which is then sintered. The resulting metal structure has been found to be suitable for use as an electrode in a Ni-Cd cell.